The present invention relates to built-up roofing systems and methods. More particularly the invention relates to built-up roofing systems for flat or low sloped roofs utilizing a novel coal tar composition as the flood coat.
Built-up roofing (BUR) systems generally comprise a substantially rigid deck covered with a membrane comprising multiple layers of bitumen impregnated felt having a separately applied coating of bitumen on top of each layer of felt with a protective layer of small stones or other inert mineral aggregate materials embedded in and covering the top bitumen coating. BUR is used primarily on commercial buildings which have flat or low-slope roofing systems. Its popularity arises from its relatively low cost combined with its effectiveness as a water repellant membrane and its durability.
Bituminous materials, especially asphalt and coal tars, have been utilized as roofing materials particularly in built-up roofing applications, as road paving materials, and as adhesive materials. However, such materials tend to deteriorate under conditions of extreme temperature variations, constant exposure to physical stress, and environmental weathering. Various proposals have been made in the art to modify the bituminous materials to overcome these deficiencies.
Although asphalt and coal tar have a similar appearance when in a package or in a finished roof, they are derived from different raw materials, and they are also different in their chemistry. Coal tar and asphalt generally are incompatible. Coal tar is obtained by heating bituminous coal to very high temperatures and collecting the volatile materials that are produced. These volatiles are referred to as crude coke oven tar, and the solid residue left behind is called coke. The crude coke oven tar is processed to recover a variety of materials including creosote and precursors for a large number of other important chemicals. The residue left after this processing step is called coal tar pitch which comprises primarily aromatic hydrocarbons. The coal tar pitch is the material used in the more familiar applications of roofing and asphalt concrete surface treating.
Asphalt, on the other hand, is derived from petroleum or crude oil and comprises primarily aliphatic hydrocarbons. Crude oil is processed at a refinery by distilling off the xe2x80x9clight endsxe2x80x9d to produce materials such as propane, gasoline, fuel oils, and chemical intermediates. The residue that remains from the distillation is referred to as straight-run asphalt. Straight run asphalt is processed primarily for road paving applications, and after further processing (e.g., oxidation or blowing), it is converted to roofing asphalts designated as D312 Types I through IV, by the American Society for Testing and Materials (ASTM).
The present invention utilizes compositions which are prepared from coal tar as opposed to compositions which are prepared from asphalt. Aqueous coal tar emulsions have been described in the prior art as useful in preparing protective coatings. In its most common form, an aqueous coal tar emulsion comprises an emulsion of a coal tar in an aqueous medium with an emulsifying or dispersing agent such as an organic soap or detergent and/or an inorganic colloid such as a particulate clay. A conventional practice in the protective coating art is to brush, spray or paint the articles with an aqueous emulsion of coal tar. When the coating of coal tar dries on the article, it provides a protective film. Such films, however, have certain disadvantages such as being attacked by various solvents, being soft, and having inadequate ductility or tensile strength. It has been proposed to improve these properties by including various additives into the emulsions. Thermoplastic rubbers, for example, have been suggested as useful additives for coal tar emulsions to improve solvent resistance and elasticity of the film. In particular, a synthetic acrylonitrile-butadiene latex has been suggested as being useful for adding to coal tar emulsions. U.S. Pat. No. 3,027,342 describes a rubberized coal tar emulsion by dissolving a copolymer of acrylonitrile and butadiene and coal tar to form a solution which can be successfully emulsified in an aqueous medium without the addition of an emulsifying agent. U.S. Pat. No. 3,296,165 describes a coal tar emulsion composition comprising an emulsion coating including an emulsified coal tar/clay mixture and a butyl rubber latex. The compositions described in the ""165 patent also include an aluminum powder additive.
U.S. Pat. No. 3,497,371 describes coal tar emulsions containing certain filler materials, a synthetic rubber latex, and certain water-soluble organic amines.
U.S. Pat. Nos. 3,835,117 and 3,897,380 describe rubberized coal tar emulsion compositions especially suitable for sealing bituminous pavement compositions such as asphalt pavement compositions. The rubberized coal tar emulsions described in these two patents are comprised of a major portion of a prepared coal tar pitch emulsion and water and a minor portion of an acrylonitrile-butadiene copolymer latex having an average particle size between 400 and 1000 angstroms, and, optionally, a silicone resin.
U.S. Pat. No. 4,544,690 also describes aqueous rubberized coal tar emulsions. The coal tar emulsions described in this patent comprise a major portion of a commercial coal tar emulsion and water admixed with a small amount of a carboxylated butadiene-styrene-acid copolymer latex having a particular size. The emulsions also may contain a fine mineral filler material such as sand. Such emulsions are reported to exhibit a high degree of spreadability, and to provide a sealing coating that has a long life.
U.S. Pat. Nos. 4,835,199 and 4,973,615 describe bituminous compositions comprising a blend of bitumen (including asphalts and tars) and a thermoplastic elastomer containing at least two polymer blocks wherein one of said polymer blocks is a crystalline polymer block and one of said polymer blocks is an amorphous polymer block. Examples of such thermoplastic elastomers include styrene-butadiene block copolymers. The compositions described in the ""615 patent also include a polyolefin.
In one embodiment, this invention relates to a bitumen-based built-up roofing system comprising a structural deck covered with a membrane comprising:
(A) at least two layers of reinforcement, the bottom layer being attached to said structural deck,
(B) a bitumen-based waterproofing adhesive between each layer of reinforcement wherein each layer is adhered to the bitumen-based adhesive between the layers,
(C) a bitumen based flood coat over the reinforcement layers, and
(D) a protective layer of mineral aggregate material embedded in the flood coat, wherein the bitumen in at least the flood coat comprises a coal tar composition prepared from a blend comprising:
(1) from about 80 parts to about 98 parts by weight of coal tar having an overall float test of from about 50 seconds to about 220 seconds,
(2) from about 2 parts to about 20 parts by weight of coal tar pitch having a softening point of from about 140 to about 160xc2x0 C., and
(3) from about 1% to about 20% by weight, based on the total weight of the composition, of an acrylonitrile-butadiene copolymer.
In another embodiment, the present invention relates to a coal tar impregnated reinforcement sheet useful particularly in bitumen-based built-up roofing systems which comprises a layer of reinforcement such as a felt which has been impregnated with a coal tar composition as described above.
In yet another embodiment, the invention relates to a method of re-coating a bitumen-based built-up roofing membrane which comprises the steps of:
(A) removing loose mineral aggregate, if any, from the surface of the existing roofing membrane,
(B) cleaning the surface of an existing roofing membrane,
(C) applying a flood coat over the cleaned surface, and
(D) embedding a layer of mineral aggregate material into the flood coat wherein the flood coat comprises the coal tar composition as described above.
The invention also relates to a method of re-coating a built-up roofing system having a mineral-surfaced cap sheet which comprises the steps of:
(A) cleaning the surface of the mineral-surfaced cap sheet of an existing roofing membrane,
(B) applying a flood coat over the cleaned surface,
(C) embedding a layer of mineral aggregate material into the flood coat wherein the flood coat comprises the coal tar composition described above.
A method of re-covering a bitumen-based built-up roofing membrane is also described which comprises the steps of:
(A) removing loose mineral aggregate or mineral surfacing, if any, from the upper surface of the existing roofing membrane,
(B) cleaning the upper surface of the existing roofing membrane,
(C) applying one or more layers of reinforcement, the bottom layer being attached to the cleaned upper surface of the existing roofing membrane,
(D) applying a bitumen-based waterproofing adhesive between each layer of reinforcement when more than one layer is applied, and between the bottom layer of reinforcement and the cleaned upper surface of the existing roofing membrane, wherein each reinforcement layer is adhered to the bitumen-based adhesive applied between the layers, and the bottom layer of reinforcement is adhered to the cleaned surface of the existing membrane,
(E) applying a bitumen-based flood coat over the applied reinforcement layer or layers, and
(F) embedding a protective layer of mineral aggregate material into the flood coat, wherein the bitumen in at least the flood coat comprises a coal tar composition as described above.
The present invention is directed to bitumen-based built-up roofing systems, coal tar impregnated reinforcement sheets useful particularly in built-up roofing systems, methods of re-coating a bitumen-based built-up roofing membrane and methods for re-covering a bitumen-based built-up roofing membrane, all of which are described more fully below, wherein the bitumen in at least the flood coat utilized in the roofing systems and methods comprises coal tar compositions prepared from a blend of materials comprising coal tar, coal tar pitch having certain characteristics, and an acrylonitrile-butadiene copolymer. The coal tar compositions utilized in the present invention are substantially free of water, i.e., they contain less than 0.5% of water. The coal tar compositions, in one embodiment, also are substantially free (i.e.,  less than 1% w) of sand or other particulate fillers.
The first ingredient of the coal tar compositions used in the present invention is coal tar. The coal tar which is utilized in the coal tar compositions is a coal tar having a float test of from about 50 seconds to about 220 seconds as determined by ASTM Test D139 entitled Test Method for Float Test for Bituminous Materials which is commonly used for testing the viscosity of semi-solid bituminous material. Such coal tars are of the types conventionally designated as RT-7 to RT-12 coal tars. The coal tars with the higher viscosity ranges such as RT-11 and RT-12 coal tars are preferred, and the most preferred coal tar at the present time is the RT-12 coal tar. RT11 has a float test of 100 to 150 seconds at 50xc2x0 C. and RT12 has a float test of 150-220 seconds at 50xc2x0 C. The standard specification for these and other road tars is found in ASTM D490-92. The RT-11 and RT-12 coal tars contain no water and have a minimum specific gravity at 25/25xc2x0 C. of 1.16.
In one embodiment, up to about 35 parts by weight of the coal tar normally present in the blend can be replaced by coal tars designated by ASTM D450, Types I and Ill. These have respective softening points (ASTM D36) of 52xc2x0 C. to 60xc2x0 C. and 56xc2x0 C. to 64xc2x0 C.
A second ingredient of the blend of the coal tar compositions is a coal tar pitch having a softening point of from about 140xc2x0 C. to about 160xc2x0 C. More often, the coal tar pitch will have a softening point of from about 145xc2x0 C. to 155xc2x0 C. and most often in the range of from about 148xc2x0 C. to about 152xc2x0 C. The softening point of the coal tar pitch can be determined by ASTM Test designations D-36, D3104 or D3461. Such coal tar pitches are available commercially, and one source is the Smith Facing and Supply Company, Cleveland, Ohio as flaked coal tar pitch.
A third ingredient of the blend used to prepare the coal tar compositions is a copolymer of acrylonitrile and 1,3-butadiene. Generally, the copolymers will be comprised of a major amount of butadiene and a minor amount of the acrylonitrile. Minor amounts of other monomers may also be present, but the copolymers are preferred. In another preferred embodiment, the copolymers are not cross-linked. The acrylonitrile content of the copolymer may range from about 20% to about 40 or 45% by weight, although it is preferred that the acrylonitrile content of the copolymer is between about 25% to about 35% by weight. As the acrylonitrile content increases, it becomes increasingly more difficult to dissolve the copolymer in the tar. The acrylonitrile-butadiene copolymers also may be characterized as having a Mooney viscosity (ML-4 at 100xc2x0 C.) in the range of from about 25 to about 100 as determined by ASTM D1646. More often, the Mooney viscosity will be in the range of from about 25 to about 85. Blends of two or more acrylonitrile copolymers also can be utilized to provide coal tar compositions having the desired properties. Useful acrylonitrile-butadiene copolymers are available commercially from, for example, the Chemical Division of Goodyear Tire and Rubber Company, Akron, Ohio under the general trade designation Chemigum, and Zeon Chemicals Inc., Louisville, Ky. under the general trade designation Nipol. Examples of acrylonitrile-butadiene copolymers which are commercially available from Goodyear in bale form include those Chemigum products identified in the following table.
Some of the copolymers listed in Table I also are available from Goodyear in powder form and these are identified with a P in place of the N.
The acrylonitrile-butadiene copolymers may contain other materials such as partitioning agents. Examples of useful partitioning agents include polyvinyl chloride and inorganic materials such as powdered calcium carbonate. The amount of partitioning agent present in the acrylonitrile-butadiene copolymers may vary over a wide range although it is generally preferred that the amount of partitioning agent be within the range of from about 5 to about 15% by weight.
As mentioned above, the coal tar compositions useful in the present invention are prepared from a blend comprising the three ingredients described above and the optional coal tar pitch having a softening point in the range of 52-60xc2x0 C., described above. Generally, the coal tar compositions are prepared from a blend comprising
(A) from about 80 to about 98 parts. by weight of the coal tar having an overall float test of from about 50 seconds to about 220 seconds,
(B) from about 2 to about 20 parts by weight of coal tar pitch having a softening point of from about 140xc2x0 C. to about 160xc2x0 C., and
(C) from about 1 to about 20% by weight, based on the total weight of the composition, of an acrylonitrile-butadiene copolymer.
In one embodiment, the blend comprises a mixture of from about 86 to about 98 parts by weight of the coal tar. In another embodiment, the blend comprises from about 5 to about 18 parts by weight more often from about 7 to about 13 parts by weight of the coal tar pitch, and in a further embodiment, the blend comprises from about 5 to about 15% by weight, based on the total weight of the composition, of the acrylonitrile-butadiene copolymer.
As discussed above, up to about 35 parts by weight of the coal tar (A) can be replaced by a coal tar having a softening point in the range of 52xc2x0-60xc2x0 C. or 56xc2x0 C. to 64xc2x0 C. In this embodiment, the coal tar compositions may comprise
(A) from about 50 to about 98 parts by weight of coal tar having an overall float test of from about 50 seconds to about 220 seconds,
(B) from about 0 to about 35 parts by weight of coal tar selected from coal tars having softening points of about 52xc2x0 C. to 60xc2x0 C. and 56xc2x0 C. to 64xc2x0 C.,
(C) from about 2 to about 20 parts by weight of coal tar pitch having a softening point of from about 140xc2x0 C. to about 160xc2x0 C., and
(D) from about 1 to about 20% by weight of an acrylonitrile-butadiene copolymer.
The coal tar, coal tar pitch and acrylonitrile-butadiene copolymer can be blended by any of the known methods used for blending bituminous materials. The order of blending is not critical, although it is preferred first to add the coal tar pitch to the coal tar in a high shear mixing apparatus, and after this mixture is blended and the coal tar pitch is dissolved in the coal tar, the acrylonitrile-butadiene copolymer is added to the hot blended mixture of the coal tar and coal tar pitch in the high shear mixing apparatus which will reduce the copolymer into smaller particles as they are being dispersed into the hot coal tar/pitch mixture. Alternatively, the coal tar and acrylonitrile-butadiene copolymer can be blended followed by the coal tar pitch. It is important that the mixing apparatus should be of the type, which is capable of drawing the lighter weight materials (e.g., the coal tar pitch and the acrylonitrile-butadiene copolymer) into the liquid coal tar. For example, a variety of known stator-rotor and disperser blade units can be used successfully to achieve this result. If this result is not achieved, the light weight materials will float on top and will not be incorporated into the product.
Thus, in one embodiment, the coal tar compositions used in the present invention may be prepared by the process which comprises the steps of
(A) preparing at an elevated temperature, a first mixture comprising
(A-1) from about 80 parts to about 98 parts by weight of coal tar having an overall float test of from about 50 seconds to about 220 seconds, and
(A-2) from about 2 parts to about 20 parts by weight of coal tar pitch having a softening point of from about 140xc2x0 C. to about 160xc2x0 C.,
(B) maintaining the first mixture at a temperature of at least about 170xc2x0 C.,
(C) adding to the first mixture, from about 1 to about 20% by weight, based on the total weight of the composition, of an acrylonitrile-butadiene copolymer and
(D) mixing the copolymer into the second mixture.
The coal tar (A-1) and the coal tar pitch (A-2) generally are heated to a temperature of at least about 170xc2x0 C., preferably from about 180xc2x0 C. to about 200xc2x0 C. prior to mixing in step (A). After all of the coal tar pitch (A-2) is added to the coal tar (A-1) in step A, the mixture is subjected to high shear mixing at elevated temperature to ensure that the pitch is thoroughly blended and dissolved in the coal tar. Thus, mixing is continued in step (B) for a period of from about 3 to about 10 minutes or more. The mixture in step (B) preferably is maintained at a temperature in the range of from about 160xc2x0 C. to about 200xc2x0 C., and more often, in the range of from about 165xc2x0 C. to about 185xc2x0 C.
The acrylonitrile-butadiene copolymer is added to the first mixture with high shear mixing to form a second mixture while maintaining the second mixture at a temperature of at least about 160xc2x0 C. and preferably at a temperature of from about 170xc2x0 C. to about 185xc2x0 C. After all of the copolymer is added, the second mixture is maintained at the above indicated temperatures for about 30 minutes to 1.5 hours. Successful completion of the mixing process is determined in one embodiment by determining that the softening point of a sample of the blended product is in the desired range of about 55xc2x0 C. to about 70xc2x0 C., and more often in the range of about 57-64xc2x0 C. If the softening point is lower than desired, the softening point can be raised by adding a small amount (e.g., 2.5% w) of the coal tar pitch or of the acrylonitrile-butadiene copolymer (e.g., 1% w) and mixing for an additional 10 to 20 minutes.
In one embodiment, the coal tar compositions used in the present invention generally are characterized as having a Ring and Ball softening point (ASTM D36) of between about 55xc2x0 C. and 70xc2x0 C., a penetration range at 25xc2x0 C. (ASTM D5) of from about 30 to about 90 units, and more often, from about 35 to about 60 units; an elongation (ASTM D412) of at least 800%, preferably from about 800 to about 1500%, and typically at least about 1000%; a tensile strength (ASTM D412) of at least 25 psi, preferably from about 25 to about 100 psi, and typically at about 50 psi; and a cold temperature bend, 1 inch Mandrel (ASTM D3111) of at least about xe2x88x921xc2x0 C. (30xc2x0 F.) more often from about xe2x88x921xc2x0 C. to 10xc2x0 C. (30xc2x0-50xc2x0 F.), and typically, about 2xc2x0 C. (about 35xc2x0 F.). In another embodiment, the coal tar compositions of the present invention are characterized as having a softening point in the range of from about 57xc2x0 C. to about 64xc2x0 C. (135-148xc2x0 F.).